Conjugated polymer films have applications in photovoltaic devices such as solar cells. Conjugated polymer films, like films of other polymers are typically fabricated from a solution containing a conjugated polymer material dissolved in a solvent. The solution is spread onto a substrate in a thin layer and the solvent is allowed to evaporate leaving behind the conjugated polymer material.
It is often desirable to fabricate an organic bi-layer photovoltaic device using two or more different conjugated polymer films in adjacent layers. In principle, a first conjugated polymer film would be formed on a substrate using a first solution. Then a second film would be formed on the first using a second solution. Unfortunately, it is often the case that the solvent used in the second solution tends to dissolve the first conjugated polymer film.
Presently, there are only two methods for making organic bi-layer photovoltaic device. The first method uses evaporation deposition of one or more of the conjugated polymers. Unfortunately, this is a more costly and complicated procedure. The second method is to deposit a second film using a solvent that does not disrupt the first film but still dissolves the second precursor while wetting the first film. Unfortunately, it is extremely difficult to find a solvent that will wet an organic film without dissolving it.
Thus, there is a need in the art, for a method of immobilizing an organic film so that subsequent exposure to a solvent will not disrupt the film.